Frame shuttering scheme for increased frame rate

ABSTRACT

Charge is integrated in N&gt;=2 different groups within a frame buffer to form multiple image fields.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of the U.S. Provisional application Ser. No. 60/184,202, filed on Feb. 22, 2000.

BACKGROUND

[0002] Active pixel sensors, such as described in U.S. Pat. No. 5,471,215, enable acquisition of images at relatively higher rates. Different pixel circuits have been designed which enable acquiring images at even higher rates. This can enable obtaining image information after a short time of integration, and hence allow very fast snapshots to be taken with such a sensor. The integration times for such a sensor may be considerably shorter than the time it takes to read out a frame, called the “frame readout time”. Fast-moving images, therefore, are effectively frozen in time.

[0003] A limit on the speed of such a system may be set by the time it takes to read out the entire active pixel array, which may include more than one million pixels. This read out time is typically at least 100 times the length of the frame integration time.

SUMMARY

[0004] The inventors have found that the relatively long read out time may prevent capturing multiple images at short time separations. The present application teaches a technique of dividing certain kinds of resolution of the image into multiple different read out images, in order to obtain faster image read out.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] These and other aspects of the invention will be described in detail with reference to the accompanying drawings, wherein:

[0006]FIG. 1 shows a block diagram of a first embodiment which uses a divide by two scheme;

[0007]FIG. 2 shows a block diagram of the second embodiment which uses a divide by n scheme.

DETAILED DESCRIPTION

[0008]FIG. 1 shows an embodiment of the present system. A simplified active pixel array 100 is shown in FIG. 1. While the array shown in FIG. 1 has only four pixels, it should be understood that the actual array may have many more pixels, upwards of one million pixels. In the present embodiment, a resolution of an output image is divided by two in order to speed up the read out.

[0009] The active pixel sensor includes a plurality of pixels such as 104. Each pixel includes a photoreceptor 120, e.g., a photodiode or a photogate, and a control part 122. The control part may include an in pixel follower circuit 124, and a pixel selector circuit 126. The selector circuit is actuated in order to couple charge from the pixel 102 to an output line shown as 128.

[0010] A standard frame shutter operates by controlling each of a plurality of timing lines for each row of the active pixel sensor simultaneously. The integration time for each row becomes identical.

[0011] The present system operates in a different way. The pixels are divided into groups. In the embodiment of FIG. 1, there are two groups, which include even pixels and odd pixels. FIG. 1 shows the even pixels 102,106, and the odd pixels 104,108.

[0012] A controller 110 controls the integration and read out. The row drivers within the controller 110 operate to allow one set of timing for the even grouped pixels 102,106. As shown, the readout line 112 controls all of the even grouped pixels at the same time.

[0013] A separate timing, controlled by readout line 114, is used for the odd grouped pixels.

[0014] After each integration time, the results are read out using the standard CMOS active pixel sensor row-wise operation. The read out image includes two interleaved images. Each interleaved image has half of the vertical resolution of the sensor, but occurs at a much faster readout time.

[0015] The two interleaved images are coupled to an image processor 200, which can be a processor that separates the two images using software to separate the even-based image from the odd-based image.

[0016] An alternative provides a modified readout control in the controller 110. In this modified system, first the even group is read out, then the odd group. This directly produces the two interleaved images, and eliminates any need for later reconstruction of the two images.

[0017] The FIG. 1 embodiment describes dividing the resolution and hence time to read by two. More generally, it is preferred that each two adjacent pixels integrate at a different time. An alternative embodiment shown in FIG. 2 allows dividing by n. Each of n groups of the active pixel array is sampled at a specific time. The active pixels 202, 204, 206 and 208 correspond to pixel 1-pixel n. This provides separate timing control lines. A first timing control line 210 is for pixel 0, and pixel n, pixel 2n, and so on. The next timing control signal 212 goes to row 1, row n+1 plus one . . . The last timing control lines 214 controls row n-1, 2n−1 . . . The readout image has a vertical resolution which is reduced by the factor of n.

[0018] In this embodiment, the readout can occur in the order of the images, that is in the order 0, n, 2n . . . for the first image, then 1, n+1, 2n+. . . in order to allow the multiple images to be read out sequentially. When read out in this way, the first resolution divided image will be obtained first, followed by the second resolution divided image.

[0019] Alternatively, the FIG. 2 embodiment can read out all images in pixel order in the usual way, and use an image processor 220 to separate the n images.

[0020] Although only a few embodiments have been disclosed in detail above, other modifications are possible. All such modifications are intended to be encompassed within the following claims.

[0021] Other embodiments are within the disclosed invention. 

What is claimed is:
 1. An apparatus, comprising: an array of photoreceptor pixels, each pixel of the array including a photoreceptor part and control part which selects some aspect of an associated photoreceptor pixel for readout; and a control element, which selects only specified ones of the photoreceptor pixels in a specific row for integration at any given readout time such that at least each two adjacent pixels integrate at different times.
 2. An apparatus as in claim 1 , wherein said only specified ones include only alternate ones of the photoreceptor pixels, to provide two separate image fields respectively from said array.
 3. An apparatus as in claim 1 , wherein said only specified ones include one pixel out of every N pixels in said array, to provide N separate image fields respectively.
 4. An apparatus as in claim 1 , further comprising an image processor, separating said specified groups of photoreceptor pixels into separate image fields, and providing respective outputs indicative of said separate image fields.
 5. An apparatus as in claim 2 , further comprising an image processor, receiving a pixel stream including two interleaved images and operating to separate said two image fields.
 6. An apparatus as in claim 2 , further comprising a readout system, reading out a first image field at a first time to produce a first image, and a second image field at a second time to produce a second image.
 7. An apparatus as in claim 3 , further comprising a readout system, reading out pixels from each row in a specified order in which at least one pixel in each row is skipped between each two read pixels, to read out pixels in the order 0, N, 2N . . . to provide a first image, and 1, N+1, 2N+1 to provide a next image and so one to provide the N images.
 8. A method, comprising: integrating light indicative of a scene being imaged in a plurality of pixels forming an array, said integrating comprising integrating each of said pixels in said array beginning and ending at substantially the same time but in at least two different groups; and forming at least two different image fields from the at least two different groups.
 9. A method as in claim 8 , wherein said integrating comprises integrating only certain pixels at any time, with at least one non-integrated pixel being between each integrated pixel at any integration time.
 10. A method as in claim 9 , wherein said forming comprises reading alternate pixels to provide two separate image fields.
 11. A method as in claim 9 , wherein said forming comprises reading one of every N pixels to provide N separate image fields.
 12. A method as in claim 9 , wherein said reading reads all pixels, including multiple interleaved images, and further comprising separating said multiple interleaved images.
 13. A method as in claim 9 , wherein said forming reads a single interleaved image at any time.
 14. An apparatus, comprising: an array of active pixel sensors, each including a photoreceptor portion, and a control portion, said control portion enabling activation of said photoreceptors between an integrating state and into a non integrating state, and also enabling transfer of charge from said photoreceptor to an output; and a controller, controlling said photoreceptors to integrate in a plurality of different periods, such that at least a first group of photoreceptors integrates during a different time than a second group of said photoreceptors.
 15. An apparatus as in claim 14 , wherein said plurality is two.
 16. An apparatus as in claim 14 , wherein said control portion includes a follower buffer transistor, and a selector.
 17. An apparatus as in claim 14 , wherein said controller controls said photoreceptors to produce said charge from each individual group at a time.
 18. An apparatus as in claim 14 , wherein said controller controls said photoreceptors to produce their respective charge in order, and further comprising an image processor which separates a first image field within said photodetectors from a second image field within said photodetectors. 